Thermal Energy Transfer and Equilibrium
Introduced| English |
|---|
| heat/hiːt/ |
| thermal equilibrium/ˈθɜːml ˌiːkwɪˈlɪbrɪəm/ |
| conduction/kənˈdʌkʃn/ |
| convection/kənˈvekʃn/ |
| radiation/ˌreɪdɪˈeɪʃn/ |
Hot coffee cools, cold soda warms — both meet in the middle
- Leave a hot coffee and an iced soda on the table. The coffee cools; the soda warms.
- Both drift toward the same room temperature and then stop changing.
- Heat 热量 always flows on its own from hot to cold, never the other way.
- When everything reaches one temperature, the flow stops — thermal equilibrium 热平衡.
Heat flows hot to cold
- Heat is thermal energy moving because of a temperature difference.
- It flows from the hotter object to the colder one, spontaneously.
- The bigger the temperature difference, the faster the heat flows.
- Heat is energy in transit — an object doesn't "contain heat", it contains internal energy.
Heat changes the state
Raise the temperature and watch thermal energy speed up particles and change the state of matter.
Left on their own, in which direction does heat flow?
Heat flows spontaneously from the hotter object to the colder one.
Three ways heat travels
- Conduction 传导 — through direct contact, as fast particles jostle slower neighbours (metals excel).
- Convection 对流 — warm fluid rises and circulates, carrying energy with it.
- Radiation 辐射 — infrared waves that need no medium (how the Sun warms Earth).
- All three move energy from hot to cold.
Heat transfer through direct contact between materials is called ____.
Conduction moves heat by contact; metals conduct especially well.
Radiation is the only one of the three heat-transfer methods that needs no medium.
Radiation travels as infrared waves through empty space — that is how the Sun warms Earth.
Select all genuine methods of heat transfer.
Conduction, convection and radiation carry heat. Gravitation is not a heat-transfer method.
Reaching equilibrium
- When two objects touch, heat flows until they share one temperature.
- At that point the net heat flow is zero — they are in thermal equilibrium.
- Equilibrium means equal temperature, not equal energy.
- A thermometer works by coming to equilibrium with whatever it measures.
Two objects are in thermal equilibrium when they have the same:
Equal temperature means no net heat flow — thermal equilibrium.
Thermal equilibrium means the objects reach the same temperature, not the same amount of energy. A large cool object can still hold far more internal energy than a small hot one — temperature and total energy are different things.
Thermal equilibrium means the two objects hold the same amount of internal energy.
It means equal temperature, not equal energy — a large cool object can still hold more energy.
A metal spoon at $80\ ^\circ\text{C}$ is placed in water at $20\ ^\circ\text{C}$.
- Heat flows from the hot spoon into the cooler water.
- The spoon cools and the water warms until both sit at one in-between temperature — equilibrium.
Heat is energy that flows spontaneously from hot to cold because of a temperature difference — by conduction, convection or radiation. It stops when everything reaches one temperature: thermal equilibrium, which means equal temperature, not equal energy.